Which of the following is a common symptom of recurring aphthous stomatitis?

Recurring aphthous stomatitis, often referred to as canker sores, is characterized by the formation of painful ulcers in the oral cavity. This condition primarily presents with painful sores that are usually round or oval, with a gray or white center and a red halo. The pain associated with these sores can make eating, drinking, and even speaking uncomfortable for those affected. This symptom is key in identifying the condition and differentiates it from other oral health issues.

While the other options present symptoms that may occur in various oral pathologies, they are not specifically associated with recurring aphthous stomatitis. For instance, dry mouth can be related to various factors, including medication side effects or dehydration, but it is not a hallmark of aphthous stomatitis. Similarly, swelling in the gums might suggest gingivitis or another form of periodontal disease, and bad breath typically stems from issues such as oral hygiene or other infections, rather than the ulcerative lesions of aphthous stomatitis. Thus, the hallmark symptom of recurring aphthous stomatitis is indeed the presence of painful sores in the mouth.